# Transformers lab report

## LAB REPORT ELECTRICAL POWER

LAB REPORT

ELECTRICAL POWER

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Experiment 1

Open circuit and short circuit tests of a single-phase transformer

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Aim

1.                  To study the variation of iron loss and no load current with the applied voltage

2.                  To determine the equivalent circuit parameters of the single phase transformer

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Apparatus

1.                  (100VA, 240/110) single phase transformer               1 no.

2.                  (0-250V, AC) voltmeter                                             1 no.

3.                  (0-150V, AC) voltmeter                                             1 no.

4.                  (0-1A, AC) ammeter                                                   1 no.

5.                  Wattmeter                                                                   1 no.

6.                  230/(0-250V) variac                                                    1 no.

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Theory

For a practical transformer the following features should be taken in to account:

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1.      Finite winding resistance

2.      Flux is not entirely confined to the core. Some portion appears as a leakage.

3.      It draws a finite current from the source on no load.

4.      It contains hysterisis and eddy current losses.

5.      The magnetic circuit of the transformer is not linear.

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By taking suitable steps, we can separate out those deviations in the practicle transformer and derive some relationship. We will use them to predict the performance of the transformer.

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## The exact equivalent circuit of a transformer is as shown in Figure 1

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Where

R1:       Primary winding resistance

R2:       Secondary winding resistance

X1:       Primary leakage reactance

X2:       Secondary leakage reactance

RC:       Equivalent resistance to represent Iron loss

Xm:      Magnetizing reactance

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Procedure

Part A: Open circuit test

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(a)                Examine the transformer and note down the rated voltage, KVA rating and operating frequency.

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(b)               Identify the HV side and LV side and calculate the rated currents for each side.

## (c) Connect the circuit as shown in Figure 2.

Note that the open circuit test is done on the LV side while HV side is open circuited.

(d)   Keep the variac at it's minimum position.

(e)    Switch on the power supply and raise the primary voltage to it's rated voltage.

(f)    Note down the ammeter (IOC), voltmeter (VOC) and the wattmeter (WOC) readings.

(g)   Decrease the primary voltage in steps of 10V and observe the meter readings on the given table below.

## Calculations

If:

VOC       Primary input voltage when the secondary is open circuited.

IOC        Primary current when the secondary is open circuited.

WOC      Iron loss when the secondary is open circuited.

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For rated values note down the following observations.

## More by this Author

Lukasz Kocewiak 7 years ago

I like it. For no load losses test there might be included some calculations related with magnetizing impedance.

D.Sathiyakumr 7 years ago

discussion this open circuited practical

Charles Rawlins 6 years ago

Did you measure the DC resistance of the primary?

kavan raj urs 6 years ago

dear sir i want full explantion about oc and sc test .and why it like.

salem 5 years ago

thanks i got a lot of information from this report

Rakesh 4 years ago

I got informatiom about oc test bt one doubt why we use LV side as primary.

sarang titare 4 years ago

Thanks sir for providing us detail about eqvt ckt of transformer.

but i have a one doubt.

why transformer works on only AC why not work on DC?

John 4 years ago

Why is a transformer rated in volt-ampere (VA)?